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2017 BMO TST
5
5
Part of
2017 BMO TST
Problems
(1)
Albania BMO TST Problem 5
Source:
4/1/2017
Given a set
A
A
A
which contains
n
n
n
elements. For any two distinct subsets
A
1
A_{1}
A
1
,
A
2
A_{2}
A
2
of the given set
A
A
A
, we fix the number of elements of
A
1
∩
A
2
A_1 \cap A_2
A
1
∩
A
2
. Find the sum of all the numbers obtained in the described way.
combinatorics